JP5032483B2 - Bandpass filter - Google Patents

Description

  For example, a band-pass filter that can be used in a front-end circuit is shown.

  Bandpass filters are known from the publication US 5,191,305. A filter with a delay line is known from the publication US 5301135. Transversal and recursive filters are known from publication US 5021756.

  The problem to be solved is to provide a bandpass filter with low insertion loss and a large jamming signal in the stopband.

  The bandpass filter is suitable for incorporation in a substrate on which a front end module is mounted, in particular an LTCC substrate. The front end module may be designed as a multiband module. The front-end module may be designed as a WLAN module having two frequency bands, for example, 2.4-2.5 GHz and 4.9-5.95 GHz.

  The transfer function of the bandpass filter has a steep edge.

  A band-pass filter having signal branches connected in parallel that merge into a common signal path is shown on the input side and output side.

を有する時計回りのモードと、

を有する反時計回りのモードが伝搬する。少なくとも２つの阻止周波数をもつバンドパスフィルタの出力側に生じる

については、

が成り立つ。ここで、互いに逆向きのモードの振幅はほぼ等しく

、これらのモードの位相差は１８０°である：

The two signal branches form a ring resonator in which the ring resonator

A clockwise mode having:

Propagate counterclockwise mode with Occurs at the output of a bandpass filter with at least two stop frequencies

about,

Holds. Here, the amplitudes of the opposite modes are almost equal.

The phase difference between these modes is 180 °:

  The transmission coefficient of each signal branch is equal in the conduction direction, so that two modes that are opposite to each other can circulate. These signal branches have frequency dependent delays and each act as a phase shifter. The two different signal branches preferably have different amplitude and / or phase characteristic curves.

  The ring resonator in an advantageous embodiment has a lumped LC element, ie a capacitance and an inductance. Inductance can basically be substituted in the section of the delay line or transmission line.

  However, the ring resonator may be formed only by the line segment. Line segments placed in the first and / or second signal paths may have a jump in impedance. This can be generated, for example, by a stub at an appropriate position in the line segment.

  The supplied electromagnetic wave is divided into a wave component incident clockwise and a wave component incident counterclockwise at the input nodes of the first signal branch and the second signal branch. The incident component guided to the first (or second) branch is partially reflected back to this signal branch at the output node where the signal branch joins again. The clockwise mode is the sum of the wave component incident clockwise and the reflected wave component. The counterclockwise mode is the sum of the wave component incident counterclockwise and the reflected wave component.

  In one embodiment, an LCL circuit consisting of two series inductances and a capacitance connected to ground is arranged in the first signal branch. In the second signal branch, a CLC circuit consisting of two series capacitances and one inductance connected to ground is arranged.

  In one embodiment, both the capacitive element and the inductive element are arranged in the serial branch of the first and second signal branches. In this case, it is possible to suppress the direct current component of the input signal.

  In one advantageous embodiment, a first T circuit consisting of two series inductances and a capacitance connected to ground in the first signal path, and two A second T circuit consisting of a series capacitance and one inductance connected to ground is arranged. The second signal path includes a first T circuit composed of two series capacitances and one inductance connected to the ground, and two series inductances connected to the T circuit and the ground. A second T circuit consisting of one connected capacitance is arranged.

  The first signal branch element connected to the input-side common signal path is advantageously inductive if the second signal branch element connected to the input-side common signal path is capacitive, The same applies to the reverse case.

  The first signal branch element connected to the output common signal path is advantageously inductive if the second signal branch element connected to the output common signal path is capacitive, The same applies to the reverse case.

については、

が成り立つ。ここで、互いに逆向きの信号の振幅はほぼ等しく、位相差は正確に１８０°である：

信号分岐の振幅特性曲線と位相特性曲線は、有利には、バンドパスフィルタの通過帯域の両側に阻止周波数が位置し、フィルタの伝達特性曲線が急峻なエッジを有するように、選ばれている。 Occurs on the output side of a bandpass filter with at least three stop frequencies

about,

Holds. Here, the amplitudes of the signals in opposite directions are approximately equal and the phase difference is exactly 180 °:

The amplitude characteristic curve and the phase characteristic curve of the signal branch are advantageously chosen so that the stop frequency is located on either side of the passband of the bandpass filter and the transfer characteristic curve of the filter has a steep edge.

については、

が成り立つ。ここで、互いに逆向きの信号の振幅は正確に等しく、位相差はほぼ１８０°である：

Occurs on the output side of a bandpass filter with at least three stop frequencies

about,

Holds. Here, the amplitudes of the opposite signals are exactly equal and the phase difference is approximately 180 °:

Advantageously, at least two frequencies outside the stopband, the amplitudes of the opposite wave components are equal and the phase difference is 180 °. That is,

  The harmonics of the center frequency of the bandpass filter can be arranged in the vicinity of the stop band or the stop frequency. This is particularly advantageous in the case of a bandpass filter provided for the transmission path.

  Another circuit such as a balun or an impedance converter may be arranged in the path on the input side and / or output side of the bandpass filter. Advantageously, this further circuit includes a lumped element.

The bandpass filter is advantageously realized in the substrate, for example in the LTCC substrate, by means of conductive paths and conductive surfaces, in which the metallization surface of the substrate is formed. A dielectric layer (a ceramic layer in the case of an LTCC substrate) is disposed between the two metallization surfaces.
Hereinafter, the band-pass filter will be described based on a schematic diagram that is not drawn to scale.

FIG. 1A shows a bandpass filter with two T circuits having two signal branches connected in parallel,
FIG. 1B shows the bandpass filter according to FIG. 1A with the measuring device arranged in the signal branch,
FIG. 2 shows a band pal filter with four T circuits, with two T circuits per signal branch,
FIG. 3 shows the control parameters on the input and output sides of the filter according to FIG. 1A (top), the amplitude characteristic measured at the port of the measuring device (center), and the phase characteristic measured at the port of the measuring device (bottom) And
4 shows a perspective view of the metallization surface of a substrate incorporating the filter according to FIG.
FIG. 5 shows an embodiment in which the layer structure according to FIG. 4 is divided into two adjacent parts.

  The filter shown in FIG. 1A includes a signal path disposed between the input gate terminal IN and the output gate terminal OUT of the filter. This signal path includes signal branches 11 and 12 (series branches) connected in parallel. Each branch contains one circuit, which here contains only passive electrical elements, i.e. it contains capacitance and inductance and possibly line segments and does not contain semiconductor elements such as amplifier elements. Thereby, since each signal branch becomes complementary, that is, the transfer characteristics are equal in both directions, the electromagnetic wave can propagate in the closed circuit formed by two branches connected in parallel. This circuit is preferably an oscillating circuit or a ring resonator.

  The first branch 11 includes one T circuit having two series capacitances C1, C3 and one parallel inductance L2. The second branch 12 includes one T circuit having two series inductances L1, L3 and one parallel capacitance C2. The series capacitance and the series inductances C1, C3, L1, and L3 form one ring resonator, and electromagnetic waves can circulate in the ring resonator.

として計算される。ここで、ｔは時間である。周波数領域においてこれに相応する伝達特性Ｓ₂₁（ｆ）は

として計算される。ここで、ｆは周波数であり、Ａ_nは第ｎ分岐の伝達関数である。 In the case of N serial branches connected in parallel, the signals supplied to the input side are separated into N parts and merged again on the output side. Each signal branch a delay line for the corresponding partial signal, tau _n is the delay time of the signal in the n branch, is a _n is the transmission coefficient of the n-th branch. The resulting time signal y (t) is

Is calculated as Here, t is time. The corresponding transfer characteristic S ₂₁ (f) in the frequency domain is

Is calculated as Here, f is a frequency, and _An is a transfer function of the nth branch.

  It is advantageous if the amplitude characteristics (and / or phase characteristics) of the different series branches of the filters are different from one another. These amplitude characteristics may be adapted to each other such that the transfer function of the entire filter forms a passband in a predetermined frequency region and a notch at a predetermined stop frequency.

Incident electromagnetic wave is supplied to the input side IN is node 1 in clockwise incident component U _{cw, inc} and counterclockwise incident component U _ccw, divided into _inc.

Part of the component U _{cw, inc} enters the serial branch 12 at node 2, some of these components are output coupled to the output path, and some are reflected back to the branch 11, counterclockwise reflected components U _{ccw, ref} is formed. Part of the component U _{ccw, inc} enters the serial branch 11 at node 2, some of these components are output coupled to the output path, and some are reflected back to the branch 12, causing a clockwise reflected component U _{cw, ref} is formed.

The sum of all clockwise wave components forms the clockwise mode U _cw .

ｋはモードの成分のインデックスである。反時計回りのすべての波動成分の和が反時計回りのモードＵ_ccwを形成する。

k is the index of the mode component. The sum of all counterclockwise wave components forms the counterclockwise mode U _ccw .

出力ノード２に生じる信号

はこのノードにおける互いに逆向きのモードのベクトル和である：

Signal generated at output node 2

Is the vector sum of the opposite modes at this node:

のこの周波数における振幅特性と位相特性に依存する。フィルタ伝送特性の急落であるノッチは、例えば、出力ノード２において互いに逆向きのモードのベクトル和がゼロに等しくなる周波数に形成される：

。これは、互いに逆向きの２つの

The magnitude of the signal generated at a given frequency is opposite to each other

Depends on the amplitude and phase characteristics at this frequency. The notch, which is a sharp drop in the filter transmission characteristics, is formed at a frequency at which the vector sum of the opposite modes at the output node 2 is equal to zero, for example:

. This is two opposite directions

これは信号分岐が通過周波数において互いに異なる伝達係数を有する場合である。 Transmission occurs when the opposite modes have different amplitudes at node 2 and the sum of the amplitudes is not equal to zero:

This is the case when the signal branches have different transfer coefficients at the pass frequency.

  The complex amplitudes of the incident wave and the reflected wave are measured by an ideal measuring device having a part M1 arranged in the first signal branch and a part M2 arranged in the second signal branch. The signal passes through this measuring device without loss.

  Each part of the measuring device measures the sum of all wave components traveling in a predetermined direction-clockwise or counterclockwise. The measurement results are shown in the center and bottom of FIG.

Between node 1 and node 3, the wave component U _cw, amplitude characteristics S ₃₁ and the phase characteristics phi ₃₁ of _inc is detected. Between nodes 1 and 4, the wave component U _ccw, amplitude characteristics S ₄₁ and the phase characteristics phi ₄₁ of _inc is detected. Between nodes 1 and 5, the wave component U _ccw reflected at node _2, the amplitude characteristic S ₅₁ and the phase characteristics phi ₅₁ of _ref is detected, between the node 1 and node 6, it is reflected by this node The amplitude characteristic S ₆₁ and the phase characteristic φ _{61 of the} wave component U _{cw, ref} are detected.

で与えられる。 The S matrix of the measuring device is

Given in.

  FIG. 2 shows a filter with four T circuits. On the input side, a CLC circuit is arranged in the first branch 11 and an LCL circuit is arranged in the second branch 12. The CLC circuit arranged in the first branch is formed by series capacitances C1 and C3 and a parallel inductance L2. The LCL circuit arranged in the second branch is formed by series inductances L1 and L3 and a parallel capacitance C2. On the output side, LCL circuits L4, C5, and L6 are arranged in the first branch, and CLC circuits C4, L5, and C6 are arranged in the second branch.

  Similar to the bandpass filter shown in FIG. 1A, the transfer characteristic of this bandpass filter also has three notches. Furthermore, the embodiment according to FIG. 2 is excellent in that the direct current component is suppressed because the series capacitance is arranged in two series branches connected in parallel.

  In some embodiments, signal branches may be formed such that there are more than three notches in the transfer characteristic of the filter.

  The inductances arranged in at least one of the signal branches 11 and 12 of the filter, for example, the values of L1-L3 in FIG. 1A and L1-L6 in FIG. 2 may be substantially zero.

In the upper part of FIG. 3, the transfer characteristic S ₂₁ and the reflection coefficient S ₁₁ of the filter are shown. The transfer characteristic S ₂₁ shows a pass band at approximately 5.5 GHz and three notches at approximately 2.6 GHz, 7.45 GHz, and 9 GHz.

  In the element shown in FIG. 4, the filter according to FIG. 2 is realized. The LC elements arranged in the branches 11 and 12 are formed in the metallization surface of the substrate as conductive paths and conductive surfaces. The LC element, in particular the inductance, can basically also be realized by a through contact connecting the two metallization surfaces of the substrate.

  The capacitance C1 is formed between the conductive surfaces 441 and 451. The capacitance C3 is formed between the conductive surfaces 451 and 461. The inductance L2 is formed by a conductive path 421. The inductance L4 is realized by the through contact DK4. Capacitance C5 is formed between conductive surfaces 402 and 491. The inductance L6 is realized by the conductive path 481.

  The inductance L1 is realized by the conductive path 431, and the inductance L3 is realized by the conductive path 432. A capacitance C2 is formed between the conductive surfaces 401 and 411. The inductance L4 is formed by a through contact DK1 that electrically connects the conductive path 432 and the surface 452. Capacitance C4 is formed between conductive surfaces 452 and 462, and capacitance C6 is formed between surfaces 462 and 471. The inductance L5 is formed by the conductive path 482 and the through contacts DK2 and DK3.

  Conductive surfaces 401 and 402 disposed on the outer metallization surface are at ground potential and are used to shield the LC elements formed on the inner metallization surface.

  FIG. 5 shows a modified embodiment of the filter implementation shown in FIG. The layer structure according to FIG. 4 is preferably divided into two parts arranged side by side. Reference numerals 501, 502, and 503 denote electrical connections.

  The surface 401 is divided into surfaces 401 a and 401 b arranged on the metallization surface, and the surfaces 401 a and 401 b are conductively connected to each other by an electrical connection 504. The surface 402 is divided into surfaces 402a and 402b arranged on the metallization surface, and the surfaces 402a and 402b are electrically connected to each other by an electrical connection 502.

Fig. 4 shows a bandpass filter with two T circuits having two signal branches connected in parallel. 1B shows a bandpass filter according to FIG. Fig. 2 shows a band pal filter with four T circuits, with two T circuits per signal branch. 1A shows control parameters (upper) on the input and output sides of the filter according to FIG. 1A, amplitude characteristics (center) measured at the port of the measuring device, and phase characteristics (lower) measured at the port of the measuring device. Fig. 3 shows a perspective view of a metallization surface of a substrate incorporating a filter according to Fig. 2; 5 shows an embodiment in which the layer structure according to FIG. 4 is divided into two adjacent parts.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Terminal node of input side signal path 2 Terminal node of output side signal path 3-6 Port of measurement apparatus 11 First signal branch 12 Second signal branch C1-C6 Capacitance DK1-DK4 Through contact in Input side L1-L6 Inductance M1 , M2 measuring device out output side S ₁₁ , S ₂₂ reflection coefficient at node 1 S ₂₁ transfer function of circuit between nodes 1 and 2 S ₃₁ , S ₄₁ , S ₅₁ , S ₆₁ node 1 and nodes 3, 4, 5 , 6 measured transfer function φ ₃₁ , φ ₄₁ , φ ₅₁ , φ ₆₁ Phase characteristics measured between node 1 and nodes 3, 4, 5, 6 U _{cw, inc} Mode incident in clockwise direction U _{cw mode} U _ccw to reflect the _{ref clockwise} mode U _ccw incident on _{inc counterclockwise} mode which reflects the _ref counterclockwise

Claims (14)

In a bandpass filter comprising signal branches (11, 12) connected in parallel, the signal branches (11, 12) are connected to the input node (1) on the input side and to the output node (2) on the output side. A ring resonator is formed by the two signal branches (11, 12), and the inside of the ring resonator is

With clockwise mode and

Propagates in a counterclockwise mode with
Occurs at the output node (2) of the bandpass filter

For at least two stop frequencies

Where

And
The stop frequency is disposed so as pass band is formed between the two stopping frequency,
A first T-circuit consisting of two series capacitances (C1, C3) and one parallel inductance (L2), connected to the first signal branch (11), and post-connected to the first T-circuit; A second T circuit consisting of two series inductances (L4, L6) and one parallel capacitance (C5) is arranged,
A first T circuit consisting of two series inductances (L1, L3) and one parallel capacitance (C2), connected to the second signal branch (12), and post-connected to the first T circuit; A band-pass filter characterized in that a second T circuit composed of two series capacitances (C4, C6) and one parallel inductance (L5) is arranged .   The bandpass filter according to claim 1, wherein the ring resonator comprises a lumped LC element (L1-L6, C1-C6).   The bandpass filter according to claim 1 or 2, wherein the signal branch (11, 12) acts as a phase shifter. The bandpass filter according to claim 3, wherein the two different signal branches (11, 12) have different amplitude characteristic curves (S ₃₁ , S ₄₁ ) and / or phase characteristic curves (φ ₃₁ , φ ₄₁ ). The clockwise mode (U _cw ) is the sum of the clockwise wave component (U _{cw, inc} ) and the reflected wave component (U _{cw, ref} ),
5. The counterclockwise mode (U _ccw ) is a sum total of a counterclockwise wave component (U _{ccw, inc} ) and a reflected wave component (U _{ccw, ref} ). The described bandpass filter. The component of the first signal branch (11) connected to the input node (1) is inductive and the component of the second signal branch (12) connected to the input node (1) is capacitive, the opposite case is the same, the bandpass filter of any one of claims 1 to 5. The component of the first signal branch (11) connected to the output node (2) is inductive and the component of the second signal branch (12) connected to the output node (2) The bandpass filter according to any one of claims 1 to 6 , wherein is capacitive and vice versa. Occurring at the output node (2)

For at least three stop frequencies

Where

In it, a band-pass filter of any one of claims 1 7. In the amplitude characteristic curve and the phase characteristic curve of the signal branch (11, 12), the stop frequency is located on both sides of the pass band of the band filter, and the transfer characteristic curve (S ₂₁ ) of the filter has a steep edge. The band pass filter according to any one of claims 1 to 8 , which is selected as follows. Occurring at the output node (2)

In the blocking area

Where

In a bandpass filter according to any one of claims 1-9. At least two frequencies in the blocking region,

The band-pass filter according to claim 10, wherein: The bandpass filter according to claim 10 or 11 , wherein at least one harmonic of the center frequency of the bandpass filter exists in the blocking region. The band-pass filter according to any one of claims 1 to 12 , realized by a conductive path in a substrate. The bandpass filter according to claim 13 , wherein the substrate contains ceramics.

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